This invention is in the field of electronic sensors. Embodiments disclosed in this specification include electronic sensors for sensing evaporation rate and relative humidity.
Atmometers are instruments for measuring the rate at which water evaporates from a wet surface into the atmosphere. Evaporation rate and related parameters are of particular importance in agriculture, among other industries. For example, knowledge of the rate at which plants transpire can assist the scheduling of irrigation activities, both in timing and in the amount of water applied to the crops. Efficient use of available water is, of course, especially important in arid regions, or those regions experiencing drought, where ground and surface water is at a premium.
Conventional atmometers operate by measuring the rate at which water is drawn from a reservoir to a surface exposed to the atmosphere. In one type of conventional atmometer, the exposed surface is a porous ceramic plate that is connected to the water reservoir by a tube. In the agricultural context, a canvas cover is typically provided over the ceramic plate to mimic the canopy of the crop of interest. As water evaporates from the ceramic plate, additional water is drawn through the tube from the reservoir to the plate. Measurement of the water level in the reservoir over time thus provides a measurement of the rate at which water is evaporating at the ceramic plate, from which the transpiration rate of the crop plant of interest can be inferred. The frequency at which measurements can be obtained from those conventional atmometers is necessarily limited, and as such these measurements are each essentially averaged over relatively long time periods (e.g., at least a few hours). In addition, because the evaporation rate measurement is typically obtained by visual inspection of the reservoir level, these conventional atmometers are not conducive to automation.
A recent trend, however, is the increasing deployment of networked communications among computer systems and other electronic devices themselves, absent human initiation or control of the communications. These machine-to-machine (“M2M”) communications are now being carried out over a wide-area network, such a network now often referred to as the “Internet of Things” (“IoT”). In this context, the nature of the communications can differ significantly from conventional human-oriented Internet communications. The amount of data transmitted from one “machine” to another in a given transmission is often quite small (e.g., streaming video is not often involved), and is often not particularly time-sensitive. As such, the communications requirements for IoT can be somewhat relaxed. On the other hand, the number of M2M network nodes in the future is contemplated to be substantially larger than the number of nodes in the human-oriented Internet.
By way of further background, humidity is an important parameter in many industries, such as semiconductor processing, pharmaceutical and other chemical processing, petroleum refining, paper and textile production, agriculture, medicine, and food processing, to name a few. As such, conventional humidity sensors are used in equipment for these and other industries, examples of such equipment including respiratory equipment, sterilizers, incubators, ovens, dryers and dessicators, condensation prevention equipment, and monitoring equipment such as soil moisture monitors and building environmental control.
By way of further background, Gu et al., “Kinetics of Evaporation and Gel Formation in Thin Films of Ceramic Precursors”, Langmuir, Vol. 30, No. 48 (American Chemical Society, 2014), pp. 14638-47 (see “Supporting Information for Kinetics of evaporation and gel formation in thin films of ceramic precursors”, available at http://www.clemson.edu/ces/kornevlab/article/43si.pdf), describes the evaporation mechanism as a diffusion mechanism that depends on the water vapor concentration gradient between the surface of the evaporating water droplet (i.e., at 100% relative humidity) and the ambient atmosphere (i.e., at the ambient relative humidity). This mechanism is expressible as a temperature-dependent diffusion equation, from which the ambient relative humidity can be determined from measurements of the evaporation rate and the temperature.